本文試圖通過對朱子「真知」概念的內容和結構的分析，說明「真知」 概念所包含的動機效力，並藉由T. Nagel 的理論，以回應休謨式問題的詰難。 對於「知而不能行」之知，朱子認為這種知只是淺知，而真知則必能行。依 朱子，一個人在特定情境下對何為最好的知道得越深，他就越可能依其判斷 去行動，當一個人之知達到了最高的程度，他便完全會依知而行。這種知 （真知）不僅是對所當然之則之知，也是對所以然之理之知，而這種所以然 之理原在自家身心上，經由反省體驗而得，因而具有在道德行動中決定如此 而不如彼的動機效力。

This paper tries to explain the idea of motivational efficacy included in Zhuxi’s concept of “true knowledge” by analyzing the content and structure of this concept, and to face the challenge of the Humean problem through T. Nagel’s theory. For Zhuxi, the knowledge of “knowing without being able to act” (zhi er bu neng xing) is merely knowledge of a shallow kind as the true knowledge will definitely lead to action. In a given situation, the better a man knows what good is, the more likely he acts according to his judgment. When a man’s knowledge reaches the highest degree, he will completely follow it. This kind of knowledge (“true knowledge”) is not only the one that man acts according to what he knows, but also the one that man should do. The latter originates from one’s own mind, and it can be known only through self-reflection by gaining the motivational efficacy determining why a man does this way rather than the other in moral actions.